1. Technical Field
The present invention relates to device fabrication and, more particularly, to removal of scratches created during polishing.
2. Background Art
In device fabrication, insulating, semiconducting, and conducting layers are formed on a substrate or wafer. The layers are patterned to create features and spaces, forming devices, such as transistors, capacitors, and resistors. These devices are then interconnected to achieve a desired electrical function.
It is often desirable to provide a planar topography before a subsequent layer is formed. A nonplanar topography creates problems in the patterning of subsequent layers. Such problems include, for example, limited depth of focus by the photolithographic system, metal residues during reactive ion etching, and poor metal step coverage.
To provide a planar topography, planarization schemes are employed. The planarization schemes typically include polishing to remove topography, surface defects such as crystal lattice damage, scratches, roughness or embedded articles such as dirt or dust. This polishing is typically referred to as chemical mechanical polishing (CMP).
In general, the CMP process involves holding a thin flat wafer against a rotating wetted polishing surface under a controlled downward pressure. A polishing slurry such as a solution of alumina or silica may be used as the abrasive medium. A rotating polishing head or wafer carrier is typically utilized to hold the wafer under controlled pressure against a rotating polishing platen. The polishing platen is typically covered with a relatively soft wetted pad material such as a blown polyurethane.
However, CMP creates micro scratches on the surface of the layer being polished. These micro scratches are particularly problematic in interconnection schemes. For example, the scratches formed during CMP are filled with metal as the metal layer is deposited. As dimensions of feature size becomes increasingly smaller, there is a greater probability that a scratch contacting adjacent metal lines exist. The metal trapped in such a scratch creates a short between the adjacent metal lines with which it is in contact, thus rendering the device defective.
Conventionally, a touch-up CMP is employed to combat the problem of shorts caused by metal filled scratches created during CMP. Although the touch-up CMP has been effective in reducing scratches, it requires careful monitoring to prevent overpolishing. Furthermore, the additional touch-up CMP is time consuming, adding to the raw process time in producing the device.
Therefore, there exist a need to provide a planar topography without scratches efficiently and easily.